I usually use transition sentences at the ending of each of my paragraphs. One sentence can be used to help "transition" into your next topic! It allows the reader to follow all of your points in a clear manner.
A topic sentence introduces the main idea for that paragraph (pretty much summarizes the main point of the paragraph in one sentence), while a transitional sentence is usually placed before the topic sentence to ensure a smooth transition between the paragraphs and their main ideas so that the whole essay will have a better unity. To sum up, transitional sentences serve more as a link between the arguments and paragraphs and topic sentences introduce the main argument of the paragraph.
Piggybacking off of what Julia previous wrote, a topic sentence basically provides the reader digest (summarized) version of the focal point of a given paragraph. On the other hand, transition sentences are typically inserted between paragraphs. In other words, transition sentences serve as the bridge between concepts or ideas. The smoother your “bridge”, the easier it will be to jump from one idea to another without breaking the chain that connects back to the central concept or main idea.